A Yemeni policeman stands at a check point in the capital Saana on August 3, 2013. The United States issued a worldwide warning that Al-Qaeda may attack in August as it ordered shut 21 of its embassies.

An American drone strike has killed four suspected al Qaeda militants associated with the latest threat that prompted the closing of U.S. embassies across the Middle East and North Africa, according to a senior U.S. official.

"We got the operational guys we were after," the official said, referring to the four men killed in Yemen.

The strike is among the latest in an aggressive counter-terrorism campaign waged by American drones, which have killed approximately three dozen people in Yemen just over the last two weeks, another U.S. official told ABC News.

Officials later said they believed the original threat had been narrowed to a possible vehicle-borne bombing attack targeting the U.S. Embassy in the Yemeni capital of Sana'a.

The anticipated attack has not yet come to pass and all embassies except for the U.S. Embassy in Sana'a have since reopened. But even with the most recent deaths of the four militants, another U.S. official said the danger is hardly over.

"The threat remains real and serious," the official told ABC News. "We've seen nothing to indicate that it's over… [And] even if there are tactical victories, the strategic intent [to attack] will still be there."

Local news reports had raised the possibility that al Qaeda's notorious Yemen-based bomb-maker, Ibrahim al-Asiri, had been injured or killed in one of the recent drone strikes, but the U.S. official said that as of right now, there was no information to substantiate that claim.